1. Technical Field
The present invention relates to a level shift circuit that converts a logic signal into another logic signal having a different amplitude, to an electro-optical device using the same, and to an electronic apparatus.
2. Related Art
There are known electro-optical devices that display an image by using the electro-optical change of an electro-optical material, such as liquid crystal or electro-luminescent (EL) material. Among them, an active matrix electro-optical device in which pixels are driven by non-linear elements, such as transistors or diodes, can display high-quality images.
The active matrix electro-optical device has the following structure. That is, in the active matrix electro-optical device, pixel electrodes are formed at intersections of scanning lines extending in a row direction and data lines extending in a column direction, and non-linear elements, such as thin film transistors (hereinafter, referred to as TFTs), which are turned on or off in response to scanning signals supplied to the scanning lines are provided between the pixel electrodes and the data lines at the intersections. In addition, the pixel electrodes are arranged opposite to a counter electrode with an electro-optical device interposed therebetween.
However, a relatively high voltage is needed to drive the electro-optical material or the non-linear elements. Meanwhile, since an external control circuit for supplying a clock signal or control signal, which is a driving standard, to the electro-optical device is generally composed of a CMOS circuit, the amplitude of a logic input signal thereof is a voltage of about 3 to 5 V. Further, in general, in the electro-optical device, an amplitude converting circuit (hereinafter, simply referred to as a ‘level shift circuit’) that converts a low-amplitude logic input signal to a high-amplitude logic output signal is provided at an output portion of a driving circuit for driving the scanning lines and the data lines, or at an input portion for the clock signal.
Further, there is a known level shift circuit that includes first and second capacitors each having one terminal to which a signal is input, an offset circuit which offsets a voltage applied to the other terminal of each of these capacitors, and first and second switching elements which are connected to the other terminals of these capacitors (see JP-A-2003-110419). This level shift circuit can be operated at high speed with a simple structure.
The input sensitivity of the level shift circuit having the above-mentioned structure is determined by threshold voltages of the first and second switching elements. Since the threshold voltages of the switching elements are much affected by variations in a manufacturing process, the input sensitivity of the level shift circuit is also much affected by the variations in a manufacturing process. In addition, since the TFT, serving as a switching element, is formed on an insulator, the threshold voltage thereof is varied by the influence of electric charge stored when on/off operations are repeatedly performed.